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1 | #include <linux/export.h> | |
2 | #include <linux/sched/signal.h> | |
3 | #include <linux/sched/task.h> | |
4 | #include <linux/fs.h> | |
5 | #include <linux/path.h> | |
6 | #include <linux/slab.h> | |
7 | #include <linux/fs_struct.h> | |
8 | #include "internal.h" | |
9 | ||
10 | /* | |
11 | * Replace the fs->{rootmnt,root} with {mnt,dentry}. Put the old values. | |
12 | * It can block. | |
13 | */ | |
14 | void set_fs_root(struct fs_struct *fs, const struct path *path) | |
15 | { | |
16 | struct path old_root; | |
17 | ||
18 | path_get(path); | |
19 | spin_lock(&fs->lock); | |
20 | write_seqcount_begin(&fs->seq); | |
21 | old_root = fs->root; | |
22 | fs->root = *path; | |
23 | write_seqcount_end(&fs->seq); | |
24 | spin_unlock(&fs->lock); | |
25 | if (old_root.dentry) | |
26 | path_put(&old_root); | |
27 | } | |
28 | ||
29 | /* | |
30 | * Replace the fs->{pwdmnt,pwd} with {mnt,dentry}. Put the old values. | |
31 | * It can block. | |
32 | */ | |
33 | void set_fs_pwd(struct fs_struct *fs, const struct path *path) | |
34 | { | |
35 | struct path old_pwd; | |
36 | ||
37 | path_get(path); | |
38 | spin_lock(&fs->lock); | |
39 | write_seqcount_begin(&fs->seq); | |
40 | old_pwd = fs->pwd; | |
41 | fs->pwd = *path; | |
42 | write_seqcount_end(&fs->seq); | |
43 | spin_unlock(&fs->lock); | |
44 | ||
45 | if (old_pwd.dentry) | |
46 | path_put(&old_pwd); | |
47 | } | |
48 | ||
49 | static inline int replace_path(struct path *p, const struct path *old, const struct path *new) | |
50 | { | |
51 | if (likely(p->dentry != old->dentry || p->mnt != old->mnt)) | |
52 | return 0; | |
53 | *p = *new; | |
54 | return 1; | |
55 | } | |
56 | ||
57 | void chroot_fs_refs(const struct path *old_root, const struct path *new_root) | |
58 | { | |
59 | struct task_struct *g, *p; | |
60 | struct fs_struct *fs; | |
61 | int count = 0; | |
62 | ||
63 | read_lock(&tasklist_lock); | |
64 | do_each_thread(g, p) { | |
65 | task_lock(p); | |
66 | fs = p->fs; | |
67 | if (fs) { | |
68 | int hits = 0; | |
69 | spin_lock(&fs->lock); | |
70 | write_seqcount_begin(&fs->seq); | |
71 | hits += replace_path(&fs->root, old_root, new_root); | |
72 | hits += replace_path(&fs->pwd, old_root, new_root); | |
73 | write_seqcount_end(&fs->seq); | |
74 | while (hits--) { | |
75 | count++; | |
76 | path_get(new_root); | |
77 | } | |
78 | spin_unlock(&fs->lock); | |
79 | } | |
80 | task_unlock(p); | |
81 | } while_each_thread(g, p); | |
82 | read_unlock(&tasklist_lock); | |
83 | while (count--) | |
84 | path_put(old_root); | |
85 | } | |
86 | ||
87 | void free_fs_struct(struct fs_struct *fs) | |
88 | { | |
89 | path_put(&fs->root); | |
90 | path_put(&fs->pwd); | |
91 | kmem_cache_free(fs_cachep, fs); | |
92 | } | |
93 | ||
94 | void exit_fs(struct task_struct *tsk) | |
95 | { | |
96 | struct fs_struct *fs = tsk->fs; | |
97 | ||
98 | if (fs) { | |
99 | int kill; | |
100 | task_lock(tsk); | |
101 | spin_lock(&fs->lock); | |
102 | tsk->fs = NULL; | |
103 | kill = !--fs->users; | |
104 | spin_unlock(&fs->lock); | |
105 | task_unlock(tsk); | |
106 | if (kill) | |
107 | free_fs_struct(fs); | |
108 | } | |
109 | } | |
110 | ||
111 | struct fs_struct *copy_fs_struct(struct fs_struct *old) | |
112 | { | |
113 | struct fs_struct *fs = kmem_cache_alloc(fs_cachep, GFP_KERNEL); | |
114 | /* We don't need to lock fs - think why ;-) */ | |
115 | if (fs) { | |
116 | fs->users = 1; | |
117 | fs->in_exec = 0; | |
118 | spin_lock_init(&fs->lock); | |
119 | seqcount_init(&fs->seq); | |
120 | fs->umask = old->umask; | |
121 | ||
122 | spin_lock(&old->lock); | |
123 | fs->root = old->root; | |
124 | path_get(&fs->root); | |
125 | fs->pwd = old->pwd; | |
126 | path_get(&fs->pwd); | |
127 | spin_unlock(&old->lock); | |
128 | } | |
129 | return fs; | |
130 | } | |
131 | ||
132 | int unshare_fs_struct(void) | |
133 | { | |
134 | struct fs_struct *fs = current->fs; | |
135 | struct fs_struct *new_fs = copy_fs_struct(fs); | |
136 | int kill; | |
137 | ||
138 | if (!new_fs) | |
139 | return -ENOMEM; | |
140 | ||
141 | task_lock(current); | |
142 | spin_lock(&fs->lock); | |
143 | kill = !--fs->users; | |
144 | current->fs = new_fs; | |
145 | spin_unlock(&fs->lock); | |
146 | task_unlock(current); | |
147 | ||
148 | if (kill) | |
149 | free_fs_struct(fs); | |
150 | ||
151 | return 0; | |
152 | } | |
153 | EXPORT_SYMBOL_GPL(unshare_fs_struct); | |
154 | ||
155 | int current_umask(void) | |
156 | { | |
157 | return current->fs->umask; | |
158 | } | |
159 | EXPORT_SYMBOL(current_umask); | |
160 | ||
161 | /* to be mentioned only in INIT_TASK */ | |
162 | struct fs_struct init_fs = { | |
163 | .users = 1, | |
164 | .lock = __SPIN_LOCK_UNLOCKED(init_fs.lock), | |
165 | .seq = SEQCNT_ZERO(init_fs.seq), | |
166 | .umask = 0022, | |
167 | }; |